RenderTextHarfBuzz: Implement font fallback for Win and Linux

ui/gfx/font_fallback_linux.cc

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ui/gfx/font_fallback.h"
+
+#include <fontconfig/fontconfig.h>
+
+namespace gfx {
+
+std::vector<std::string> GetFallbackFontFamilies(std::string font_family) {
+  std::vector<std::string> fallback_fonts;
+
+  FcPattern* pattern = FcPatternCreate();
+  FcValue family;
+  family.type = FcTypeString;
+  family.u.s = reinterpret_cast<const FcChar8*>(font_family.c_str());
+  FcPatternAdd(pattern, FC_FAMILY, family, FcFalse);
+  if (FcConfigSubstitute(NULL, pattern, FcMatchPattern) == FcTrue) {
+    FcDefaultSubstitute(pattern);
+    FcResult result;
+    FcFontSet* fonts = FcFontSort(NULL, pattern, FcTrue, NULL, &result);
+    if (fonts) {
+      for (int i = 0; i < fonts->nfont; ++i) {
+        char* name = NULL;
+        FcPatternGetString(fonts->fonts[i], FC_FAMILY, 0,
+            reinterpret_cast<FcChar8**>(&name));
+        if (fallback_fonts.empty() || fallback_fonts.back() != name)
+          fallback_fonts.push_back(std::string(name));
+      }
+      FcFontSetDestroy(fonts);
+    }
+  }
+  FcPatternDestroy(pattern);
+
+  if (fallback_fonts.empty())
+    fallback_fonts.push_back(font_family);
+
+  return fallback_fonts;
+}
+
+}  // namespace gfx